Purification of pyrethrum extract



Paterited Mar. 27, 1945 PURIFICATION OF PYRETHRUM EXTRACT William F. Barthel, College Park, Md., and Herbert L. J. Haller, Washington, D. 0., designers to the United States of America as represented by Claude R. Wiclrard, Secretary of l lculture, and his successors in oiilce No Drawing. Application May 16. 1944,

Serial No. 535,846

I 6Claims. (Ci 260-468) (Granted under the act or March 3,1883, as amended April 30, 1928; 370 0.- G. 757) This application is made under the act of March 3, 1883, as amended by theact of April 30,

' 192a. and the invention herein described, it patented, may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to us of any royalty thereon.

This invention relates to the purification of relatively impure pyrethrum extracts, containing as active ingredients Pyrethrin I and Pyrethrin II and also variable amounts of extraneous matter, and has among its objects the production of a concentrate having a high percentage of pyrethrins and which is readily soluble in dichlorodifluromethane for purposes as disclosed in United States Patent No. 2,321,023, for example, and which, when dissolved in the dichlorodifiuoromethane, may be used in aerosol dlspersers without clogging the nozzle due to the crystallization of compounds or precipitation of impurities that are present in the usual pyrethrum extracts; the removal from the impure pyrethrum extract of constituents that cause irritation and staining of fabrics when used as an aerosol; and such other objects as may be apparent from the following description and claims.

In generaLaccording to this invention, the impure pyrethrum extract, which is conventionally obtained as a solution in a hydrocarbon solvent,

' such as in refined kerosene or petroleum ether, is shaken with an organic solvent, particularly an aliphatic nitro compound having the formula RNOz, where R represents an alkyl group, such as methyl, ethyl, propyl or butyl. The aliphatic nitro compound is a solvent for the pyrethrins but not for some of the impurities, and is immiscible with the hydrocarbon solvent. The allphatic nitro compound extracts the pyrethrins and may be separated from the hydrocarbon solvent and some of the retained impurities by any conventional means such as a separatory tunnel or a centrifugal separator. By repeating the extraction several times with fresh lots of the aliphatic nitro compound, approximately 97 percent or the pyrethrins may be extracted from the starting material.

Certain impurities, however, are also soluble in the aliphatic nitro compound and are separated with the pyrethrins, necessitating additional purification. Therefore, the combined nitro com pound solutions are further purified by contacting them with. activated carbon, preferably by passing them through a tube containing the cargitro compound is readily removed by evapora- The concentrate thus obtained contains to 100 percent pyrethrins, depending on the particular type of starting material used. In case the pyrethrins content in the concentrate is less than we percent, a further purification may be effected by mixing the concentrate with a hydrocarbon centrate that remains when the hydrocarbon solvent is removed. as by evaporation, for example, is substantially pure pyrethrins.

Specific examples exhibiting the invention are given below:

Example I A sample 01 500 g. of pyrethrum extract in deodorized kerosene, containing 20 percent pyrethrins, was agitated with three successive 250 ml. portions of nitromethane, the nitromethane solutions being separated from the kerosene solutions with a separatory funnel in each instance. The separated nitromethane solutions were combined and passed through an 8 inch column of activated carbon 1 inches in diameter. The column of carbon was then washed twice with 100 ml. portions of nitromethane. The combined activated carbon-treated nitromethane solution was combined with the washings and the nitromethone was removed from the combined solutions by distillation under reduced pressure.

The resulting concentrate contained 98 percent pyrethrins as determined by the A. O. A. C. method and weighed 90 g., representing 90 per- .cent of the pyrethrins content of the starting material.

Example H pyrethrins, was treated .as in Example I, except using a 10 inch column of activated carbon.

The resulting residue contained approximately per cent pyrethrins.

This residue was thendissolved in 1 liter of petroleum ether (boiling point 30-60 0,). The petroleum ether became turbid and an oil sepabon. After the carbon treatment. the aliphatic 55 rated. After all the oil had separated. the petroleum ether solution became clear. It was separated {mm the oil, and the petroleum ether was removed from. it by distillation on a steam bath. The concentrate thus obtained weighed 170 g., and the analysis showed a- 90 per cent pyrethrins content.

Example III Example IV,

A sample or 950 ml. or pyrethrurn extract in petroleum ether (boiling point 30-6il CJ. con== taming 8.7 percent pyrethrins, was successively extracted with 200 ml., 100 mL, and 100 ml. portions of nitromethane. The nitromethane solutions which separated from the petroleum ether and retained impurltiw were combined and passed through activated carbon and concern trated as in Example I.

The concentrate thus obtained contained 68 g. of 99 percent pyrethrins representing an overall recovery of 82. per cent.

The foregoing examples are illustrative of the invention but not limiting. Hydrocarbon sol= vents used with the initial material may vary over a wide boiling range and the nitromethane may be replaced by other alkyl nitro solvents; The proportion of hydrocarbon solvent and allwl nitro solvent also may be varied over a wide range, as may be the amount and kind or carbon, which may be either of animal or vegetable origin.

That this invention rests upon the combination of at least the alkyl nitro and the activated carbon treatments is shown as follows: It the nitromethane solution, after extracting the pyrethrins but before the treatment with carbon, is evaporated, a concentrate is obtained which normally contains only about 60 per cent pyrethrins and many impurities which are insoluble in dichloro difiuromethane. Also, it the pyrethrum extract in a hydrocarbon solution is treated with activated carbon without the nitromethane treatment, much of thepyrethrins is lost, and certain harmful impurities remain in solution. Consequently, neither procedure produces by itself the desired high concentration or pure pyrethrins.

On the other hand, as shown in the examples above, the combined treatment of this invention has been applied to samples containing 20 percent of pyrethrins in refined kerosene, 30 percent of pyrethrins in refined kerosene, 27 percentoi pyrethrins and oleoresin, and 7.5 per cent oi pyrethrins in petroleum ether, yielding in each case a pyrethrins concentrate of a high degree oi purity.

Having thus described the invention, what is claimed is:

1. A process of separating pyrethrins irorna solution of relatively impure pryethrum extract in a petroleum hydrocarbon solvent, comprising mixing the solution with an aliphatic nitro compound having the formula RNOz, where R represents an alkyl group, separating the aliphatic nitro compound solution from the petroleum hydrocarbon solution, and contacting the aliphatic nitro compound solution with activated carbon.

2. A process of separating pyrethrins from a solution of relatively impure pyrethrum extract in a petroleum hydrocarbon solvent, comprising mixing the solution with an aliphatic nitro connpound having the formula RNO-l, where R represents an alkyl group, separating the aliphatic nitro compound solution from the petroleum by drocarbon solution, contacting the aliphatic nitro compound solution with an activated carbon, and removing the aliphatic nitro compound from the activated carbon-treated solution to obtain a concentrate of purified pryethrins.

3. A. process of separating pyrethrins from a solution of relatively impure pyrethruni extract in a petroleum hydrocarbon solvent, comprising mixing the solution with an, aliphatic nitro compound having the formula RNOa, where R repre sents an alkyl group, separating the aliphatic nitro compound solution from the petroleum hydrocarbon solution, contacting the aliphatic nitro compound solution with activated carbon, removing the aliphatic nitro compound from the activated carbon-treated solution to obtains. concentrate, mixing the concentrate with a low boiling point hydrocarbon solvent for the pyrethrins, separating the low boiling point hydrocarbon solution from the undissolved impurities, and

evaporating the solvent to obtain a concentrate of purified pyrethrins.

4. The process of claim 1, wherein the aliphatic nitro compound is nitromethane.

5. The process of claim 1, wherein the aliphatic nitro compound is nitroethane. 

